Since someone already commented on Iowa, I'll comment on Nebraska. The state association uses 3-whistle for the entire postseason, districts all the way to state. Regular season is pretty much on a conference or per school basis. The Metro Conference in the Omaha metro area uses 3-whistle for all varsity games they schedule, regardless if they are conference games or not. I believe the bigger schools in Lincoln are using 3-whistle, and more schools are warming up to the idea. Everything below varsity is still 2-whistle.